Organic pigment fine particles and method of producing the same

ABSTRACT

According to the method of producing organic pigment fine particles of the present invention, when producing organic pigment fine particles by allowing two or more solutions at least one of which is an organic pigment solution in which an organic pigment is dissolved to flow through a microchannel, the organic pigment solution flows through the microchannel in a non-laminar state. Accordingly, the contact area of solutions per unit time can be increased and the length of diffusion mixing can be shortened, and thus instantaneous mixing of solutions becomes possible. As a result, nanometer-scale monodisperse organic pigment fine particles can be produced in a stable manner.

This application is a divisional application of U.S. application Ser.No. 11/917,069, filed Dec. 10, 2007, which was a National StageApplication based on PCT/JP2006/312083, filed Jun. 9, 2006, whichclaimed priority to JP 2005-171379, filed Jun. 10, 2005, each of whichis incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to organic pigment fine particles used forcoatings, printing ink, electrophotographic toner, ink for inkjetprinters, color filters and the like, and a method of producing thesame, particularly to a method of producing organic pigment fineparticles by a build-up method. More specifically, the present inventionrelates to a method of producing an organic pigment fine particledispersion by depositing organic pigment fine particles by changing thehydrogen ion exponent (pH) in the course of allowing an organic pigmentsolution to flow through a microchannel.

BACKGROUND ART

Pigments generally exhibit vivid color tone and high coloring power, andthey are widely used in many fields. Applications of pigments include,for example, coatings, printing ink, electrophotographic toner, ink forinkjet printers and color filters, and pigments have now become animportant compound indispensable in everyday life.

General properties and classification of applications of pigments aredescribed, for example, in Non-patent Document 1. Of the aforementionedapplications, ink pigments for inkjet printers and pigments for colorfilters require high performance and are practically particularlyimportant.

Although dyes have been used as a coloring material for ink for inkjetprinters, they have disadvantages in water resistance and lightresistance. To improve such problems, pigments are now being used.Images obtained using pigment ink have a special advantage that theirlight resistance and water resistance are better than those of imagesobtained by dye ink. However, formation of uniform fine particles ofpigment ink of a nanometer size which can infiltrate through spaces onthe surface of paper (i.e., monodispersing) is difficult, and thus thereis a problem that the pigment ink has poor adhesion to paper.

With an increase in the number of pixels in digital cameras, thinning ofcolor filters used in CCD sensors is in demand. Organic pigments areused in such color filters, and as the thickness of the filter dependslargely on the particle size of the organic pigment, there has been aneed to produce monodisperse and stable fine particles of a nanometersize level.

Generally, methods of producing fine particles are roughly classifiedinto breakdown methods in which fine particles are produced from a bulkmaterial by pulverization or the like as described, for example, inNon-patent Document 2 and build-up methods in which fine particles areproduced by particle growth in a gas phase or liquid phase. Although themethod of producing fine particles by pulverization based on a breakdownmethod has been frequently used and is highly practical, it involvesvarious problems such as extremely low productivity for producingparticles of organic materials of a nanometer size and limitation onmaterials to which the method can be applied. In this situation,formation of nanometer-scale fine particles of organic materials by abuild-up method is now being studied.

One of the build-up methods recently disclosed is a method for formingfine particles of an azo pigment, which is an organic pigment, usingsupercritical fluid or subcritical fluid (e.g., Patent Document 1).Specifically, the method comprises dissolving a pigment in supercriticalfluid or subcritical fluid and allowing crystal to grow by returning theconditions of the solution to room temperature and normal pressure,thereby producing fine particles. Practicing this method involvesproblems that equipment capable of giving extremely high temperature andpressure near the supercritical temperature and pressure is necessaryand that organic compounds are generally easily decomposed under suchconditions.

The second build-up method is a method for forming fine particles usinga microjet reactor, which is a micro-chemical process technologydescribed later (e.g., Patent Documents 2, 3, and 4). The methodcomprises introducing a solution in which a pigment is dissolved and amedium for deposition into two opposing nozzles of a differentmicrometer size at high pressure (e.g., 5M Pa) by a pump, verticallyinjecting gas (compressed air, etc) to the area where the jet streams ofthe two solutions collide, and discharging the pigment suspension by thegas stream (about 0.5 m³/h). Of such methods, the method described inPatent Documents 2 and 4 are equivalent to the breakdown method, inwhich pigment particles are formed into fine particles by allowingpigment suspensions to collide with each other in a chamber. On theother hand, the method described in Patent Document 3 is a method forproducing fine particles by spraying a pigment solution and a medium fordeposition in a chamber and depositing, which can be regarded as abuild-up method. The method is designed to produce particles in a narrowspace of a micrometer scale and immediately discharge the particles tothe outside of the reactor in order to prevent blocking of the reactorby the pigment fine particles. Although the method is suitable forpreparing fine particles with a narrow particle size distribution, ithas a problem that control of the contact time of solutions is difficultand thus fine control of the reaction is difficult.

The third build-up method is a method comprising gradually bringing asolution in which an organic pigment is dissolved into contact with anaqueous medium to deposit the pigment (so-called coprecipitation method(reprecipitation method)), one of the solutions containing a dispersant,thereby producing stable fine particles (Patent Document 5). Althoughparticles of a nanometer size can be easily produced by this method,there may be fluctuation in particle size or needle particles tend to beformed upon scale-up. Therefore, although particles are measured to besingle nanometer particles in a particle size measurement device, ratherlong needle particles are found when the particles are observed by atransmission electron microscope. Such particles are not suitable asfine particles for ink for inkjet printers for which spherical particlesare desirable.

There are methods classified between the build-up method and thebreakdown method. One of them is a method called conditioning, in whichthe particle size of coarse particles is made uniform by applying someenergy. Recently, a method of conditioning by heat treatment of anorganic pigment in a microreactor utilizing a concept of micro-chemicalprocess technology (described later) is disclosed (Patent Document 6).By continuously introducing a suspension of liquid pigment precursor (asolution in which pigment with a wide particle size distribution issuspended) into a microreactor to perform heat-treatment, phase changeof pigment crystal fine particles in the suspension occurs, andsimultaneously, particles having a larger average particle size and anarrower particle size distribution than those of the precursor can beproduced. The method has an advantage that particles with a narrowparticle size distribution can be obtained, but has a disadvantage thatalthough the precursor has a small particle size, the particle sizeconsequently becomes large.

Patent Document 7 discloses a method of producing a surface-treatedorganic pigment by collision mixing of an organic pigment, an aqueousmedium and a mixture containing rosin and/or a derivative of the organicpigment. To perform such collision mixing, however, use of an extremelyhigh pressure of 30 to 300 Mpa is necessary, and therefore, consideringenergy consumption, such a method of collision mixing using a microscalereactor has problems of productivity and environmental load.

[Patent Document 1] Japanese Patent Application Laid-Open No.2002-138216

[Patent Document 2] Japanese Patent Application Laid-Open No.2002-146222

[Patent Document 3] Japanese Patent Application Laid-Open No.2002-155221

[Patent Document 4] Japanese Patent Application Laid-Open No.2002-161218

[Patent Document 5] Japanese Patent Application Laid-Open No.2003-026972

[Patent Document 6] Japanese Patent Application Laid-Open No.2002-030230

[Patent Document 7] Japanese Patent Application Laid-Open No.2004-175975

[Patent Document 8] Japanese Patent Application Laid-Open No.2002-038043

[Non-patent Document 1] “Stabilization of Pigment Dispersion and SurfaceTreatment Technique/Evaluation”, 2001, pp. 123-224, TechnicalInformation Institute Co., Ltd.

[Non-patent Document 2] “The Fourth Series of Experimental Chemistry”edited by the Chemical Society of Japan, vol. 12, pp. 411-488, MaruzenCo., Ltd.

[Non-patent Document 3] W. Herbst and K. Hunger, “Industrial OrganicPigments, Production, Properties, Applications, Second CompletelyRevised Edition”, VCH A Wiley Company, 1997, pp. 595-630

[Non-patent Document 4]H. Nagasawa et. al., “Design of a New Micromixerfor Instant Mixing Based on the Collision of Micro Segments”, WILEY-VCHVerlag GmbH & Co., KGaA, Chem. Eng. Technol. 2005, 28. No. 3, p. 324-330

DISCLOSURE OF THE INVENTION Problems to be solved by the Invention

Recently, owing to the ability to perform efficient chemical reactions,techniques for performing chemical reactions using a reaction channelhaving a small channel cross sectional area, which is the so-called“micro-chemical process technology,” have been attracting attention. Themicro-chemical process technology refers to a technique of productionand chemical analysis of materials, utilizing chemical and/or physicalphenomena occurring in a microchannel having a width of several μm toseveral hundred μm formed on a solid substrate by microfabricationtechniques.

For example, Patent Document 2 describes a method for producing a disazocondensation pigment generally produced by the method of Non-patentDocument 3 in a microreactor based on the micro-chemical processtechnology. Further, Patent Document 9 describes a method for producinga diketopyrrolopyrrole pigment utilizing the micro-chemical processtechnology. These methods can be regarded as build-up methods.

In Patent Document 8, the step of synthesizing a disazo pigment isperformed in a microreactor. Since starting compounds have lowsolubility, the compounds are introduced into the microreactor in theform of a suspension. In that case, if condition control is wrong,possibility of blocking of channels becomes high. Thus, pigment fineparticles excellent in monodispersibility cannot be produced in a stablemanner, and there are problems in reproducibility and continuousproduction.

As described above, for producing organic pigment fine particlesexcellent in monodispersibility, especially for producingnanometer-scale monodisperse pigment fine particles in a stable manner,such particles cannot be produced by simply utilizing the micro-chemicalprocess technology, and further improvement in the production techniqueis required.

The present invention has been made in view of such circumstances, andaims at providing a method of producing organic pigment fine particleswhich is capable of producing nanometer-scale monodisperse organicpigment fine particles in a stable manner, flexibly adaptable totreatment conditions (e.g., different flow ratios of reaction solutionsto be mixed) and capable of processing in a large production amount. Thepresent invention also provides organic pigment fine particles producedby the method.

Means for Solving the Problems

To achieve the aforementioned object, a first aspect of the presentinvention provides a method of producing organic pigment fine particlescomprising: allowing two or more solutions at least one of which is anorganic pigment solution in which an organic pigment is dissolved toflow through a microchannel in a non-laminar state; and depositingorganic pigment fine particles from the organic pigment solution in acourse of flowing.

According to the first aspect of the present invention, an organicpigment solution is allowed to flow through a microchannel in anon-laminar state when producing organic pigment fine particles byallowing two or more solutions at least one of which is an organicpigment solution in which an organic pigment is dissolved to flowthrough the microchannel. Accordingly, the contact area of solutions perunit time can be increased and the length of diffusion mixing can beshortened, and thus instantaneous mixing of solutions becomes possible.As a result, nanometer-scale monodisperse organic pigment fine particlescan be produced in a stable manner.

The term “non-laminar flow” in the present invention means a flow withregular or irregular fluctuation, including laminar vortices representedby Karman's vortices and Taylor vortices, and turbulent flows. Thedetails of the flow are described later.

A second aspect of the present invention has a feature that, in thefirst aspect, the organic pigment solution is a solution in which anorganic pigment is dissolved in an alkaline or acidic aqueous medium,and the organic pigment fine particles are deposited by changing ahydrogen ion exponent (pH) of the organic pigment solution in the courseof flowing through the microchannel.

The second aspect defines a preferred method for depositing organicpigment fine particles from an organic pigment solution in amicrochannel. Organic pigment fine particles are deposited by changingthe hydrogen ion exponent (pH) of an alkaline or acidic organic pigmentsolution (bringing the pH to a neutral level). In this case as well, thepH of the organic pigment solution can be instantly brought to theintended pH by making the flow of the solution in the microchannelnon-laminar. Therefore, nanometer-scale monodisperse organic pigmentfine particles can be produced in a stable manner.

To achieve the aforementioned object, a third aspect of the presentinvention provides a method of producing organic pigment fine particlesincluding allowing two or more solutions at least one of which is anorganic pigment solution in which an organic pigment is dissolved toflow through a microchannel, and depositing organic pigment fineparticles from the organic pigment solution in the course of flowing,the method comprising: the step of dividing at least one solution of twoor more solutions comprising the organic pigment solution in which anorganic pigment is dissolved in an alkaline or acidic aqueous medium anda pH adjustor solution for changing a hydrogen ion exponent (pH) of theorganic pigment solution into a plurality of solutions; the step ofcombining solutions so that a central axis of at least one dividedsolution of the plural divided solutions and a central axis of anothersolution of the two or more solutions different from the one dividedsolution intersect at one point in a combining region; and the step ofdepositing the organic pigment fine particles by changing the hydrogenion exponent (pH) of the organic pigment solution by the pH adjustorsolution in the course of allowing the combined solutions to flowthrough the microchannel.

According to the third aspect of the present invention, at least onesolution of two or more solutions comprising an organic pigment solutionand a pH adjustor solution is divided into a plurality of solutions, andsolutions are combined so that the central axis of at least one dividedsolution of the plural divided solutions and the central axis of anothersolution of the two or more solutions different from the one dividedsolution intersect at one point in a combining region.

Herein, the central axis of a solution refers to, for example, thecenter line of a cylinder in the axial direction when a solution flowsthrough a channel cylindrically. When a solution indicates a centralaxis in a channel, an axis along the length direction of the channelpassing through the center of the gravity of a cross sectionperpendicular to the length direction of the channel (geometric centerof the gravity) corresponds to the central axis.

Generally, a reaction between two or more solutions in a microchannel isbasically caused by mixing by molecular diffusion. Given this, toachieve instantaneous mixing by molecular diffusion, solutions should bemixed so that the contact area of two or more solutions per unit time isincreased. Further, when two or more solutions are allowed to react,their supply flow rates into a microchannel are generally different. Ifthese two or more solutions having a different supply flow rate aredirectly supplied to a microchannel, their flow in the microchannelbecomes unstable, making the reaction unstable.

In the present invention, to solve the above problem, at least onesolution is divided into a plurality of solutions before two or moresolutions are combined, and all solutions including the plural dividedsolutions are combined in the combining step so that the central axes ofthe solutions intersect at a pre-determined intersection angle in thecombining region. Due to the combining of divided flows and contractioncaused by the change of direction of each solution flow upon combining,the contact area of solutions per unit time can be increased and thelength of diffusion mixing can be shortened, and thus instantaneousmixing of solutions can be achieved. Accordingly, by this instantaneousmixing, the pH of the organic pigment solution can be instantly broughtto the intended pH in the microchannel, and therefore nanometer-scalemonodisperse organic pigment fine particles can be produced in a stablemanner.

Further, by dividing a solution, solutions can be instantly mixed evenif a microchannel having a relatively large characteristic size is used,and therefore nanometer-scale pigment fine particles excellent inmonodispersibility can be processed in a large production amount.Moreover, by using a microchannel having a relatively largecharacteristic size, operation with low pressure loss becomes possible,and so energy-saving and eco-friendly operation can be performed.

A fourth aspect has a feature that, in the third aspect, the two or moresolutions are allowed to flow through the microchannel in a non-laminarstate.

When each solution has a high flow rate particularly upon combining inthe third aspect, those flows have high kinetic energy. As a result, asignificant contraction is generated by the change of direction of theflows, and at the same time, a convection cell is formed, in otherwords, non-laminar flows are generated. This facilitates increase in thecontact area and shortening of the length of diffusion mixing of two ormore solutions, and enables further improved instantaneous mixing.

A fifth aspect has a feature that, in any one of the first to fourthaspects, the microchannel has a characteristic length in an equivalentdiameter of 1 μm to 1000 μm.

The fifth aspect defines a preferred channel diameter of themicrochannel for practicing the present invention. The channel diameteris defined as above because a microchannel having an equivalent diameterof 1 μm or less is difficult to produce, and because an equivalentdiameter greater than 1000 μm increases the thickness of solution flowand instantaneous mixing becomes difficult. The microchannel has achannel diameter of more preferably 5 μm to 800 μm, particularlypreferably 10 μm to 500 μm in an equivalent diameter.

A sixth aspect has a feature that, in any one of the first to fifthaspects, a shear rate (1/second) represented by U/R is changed, whereinthe equivalent diameter of the microchannel is described as R(m) and amean velocity of a solution flowing through the microchannel isdescribed as U (m/second).

The sixth aspect describes a non-laminar flow with a shear rate (U/R)(1/second) as an index. By changing the shear rate (U/R) (1/second),mixing ability can be modified, and consequently the particle size oforganic pigment fine particles to be produced can be changed althoughthe change also depends on the deposition rate of organic pigment fineparticles.

A seventh aspect has a feature that, in the sixth aspect, the shear rate(U/R) is adjusted to 100 (1/second) or more. This is because when theshear rate (U/R) is adjusted to 100 (1/second) or more, instantaneousmixing is possible.

An eighth aspect has a feature that, in any one of the third to seventhaspects, an intersection angle of the central axes upon combining thesolutions is determined in the step of combining so that S1>S2 issatisfied, wherein a sum of the cross sectional areas in the thicknessdirection of all of the combined solutions is described as S1 and thecross sectional area of the microchannel in the radial direction isdescribed as S2, thereby contracting the flow of the solutions at thecombining region.

By setting an appropriate intersection angle of central axes uponcombining solutions and contracting the flow of solutions in thecombining region, the contact area of solutions can be further increasedand the length of diffusion mixing can be further shortened, makinginstantaneous mixing easier. The intersection angle can be determined bychanging the intersection angle between central axes of supply channelsof each solution combined at the combining region.

A ninth aspect has a feature that, in any one of the third to eighthaspects, a time of mixing the solutions from being combined at thecombining region and discharged through the microchannel is 1microsecond to 1000 milliseconds.

The ninth aspect defines a preferred time for instantaneous mixing forproducing nanometer-scale monodisperse pigment fine particles in astable manner. The mixing time before being discharged through themicrochannel is preferably 1 microsecond to 1000 milliseconds, morepreferably 10 microseconds to 500 milliseconds.

A tenth aspect has a feature that, in any one of the second to ninthaspects, the organic pigment solution is alkaline. Whether the organicpigment solution is acidic or alkaline is determined based on whetherthe organic pigment is homogeneously mixed under an acidic condition orunder an alkaline condition. Alkaline solutions are used becausepigments suitable for pigment ink such as quinacridone,diketopyrrolopyrrole and disazo condensation pigments are homogeneouslydissolved in alkali.

An eleventh aspect has a feature that, in any one of the first to tenthaspects, the organic pigment solution is a homogeneous solution in whichan organic pigment is dissolved in an aqueous organic solvent. This isbecause blocking of microchannels can be prevented by using ahomogeneous solution in which an organic pigment is dissolved in ahomogeneous mixed solvent of water and an organic solvent.

A twelfth aspect has a feature that, in any one of the first to eleventhaspects, the organic pigment solution contains a dispersant. This isbecause such a dispersant immediately adsorbs deposited organic pigmentfine particles and prevents the organic pigment fine particles fromcoagulating.

A thirteenth aspect has a feature that, in the twelfth aspect, at leastone dispersant is a low molecular weight dispersant. This is because,while such dispersants generally include low molecular weight or highmolecular weight dispersants such as anionic dispersants, cationicdispersants, amphoteric dispersants and pigment dispersants, lowmolecular weight dispersants prevent coagulation of organic pigment fineparticles more effectively.

A fourteenth aspect has a feature that, in any one of the first tothirteenth aspects, the organic pigment fine particles are obtained as adispersion thereof.

To achieve the aforementioned object, a fifteenth aspect of the presentinvention provides organic pigment fine particles produced by the methodaccording any one of the first to fourteenth aspects, having a modediameter of 1 μm or less.

By the method of the present invention, organic pigment fine particleshaving a mode diameter of 1 μm or less can be produced. The organicpigment fine particles are particularly excellent for ink for inkjetprinters.

ADVANTAGES OF THE INVENTION

As described above, according to the present invention, nanometer-scaleorganic pigment fine particles excellent in monodispersibility can beproduced in a stable manner. In addition, the present invention isflexibly adaptable to treatment conditions (e.g., different flow ratiosof reaction solutions to be mixed) and capable of processing in a largeproduction amount.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a flat microreactor to which the method ofproducing organic pigment fine particles of the present invention isapplied;

FIG. 2 is a schematic view illustrating a modified example of a flatmicroreactor to which the method of producing organic pigment fineparticles of the present invention is applied;

FIG. 3 is a schematic view illustrating another modified example of aflat microreactor to which the method of producing organic pigment fineparticles of the present invention is applied;

FIG. 4 is a schematic view of a three-dimensional microreactor to whichthe method of producing organic pigment fine particles of the presentinvention is applied;

FIG. 5A is a plan view of a three-dimensional microreactor;

FIG. 5B is a cross-sectional view taken on line a-a in FIG. 5A;

FIG. 6 is an explanatory view showing the relation between the shearrate and the mixing ability in the microchannel;

FIG. 7 is a graph showing the results of Example 1;

FIG. 8 is a graph comparing Example 2 and Comparative Example 2; and

FIG. 9 is an explanatory view showing the relation between the shearrate in the microchannel and the particle size of organic pigment fineparticles produced in Example 3.

DESCRIPTION OF SYMBOLS

-   10, 30 . . . microreactor-   12, 14 . . . supply channel of solution-   12A . . . divided supply channel-   16 . . . microchannel-   18 . . . combining region-   32 . . . supply block-   34 . . . combining block-   36 . . . reaction block-   38 . . . outer annular groove-   40 . . . inner annular groove-   42, 44 . . . through hole in supply block-   46 . . . combining hole (combining region 18)-   48 . . . long radial groove-   50 . . . short radial groove-   52, 54 . . . through hole in combining block-   58 . . . through hole in reaction block (microchannel 16)

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, preferred embodiments of organic pigment fineparticles and a method of producing the same of the present inventionare described in detail with reference to the attached figures.

The method of producing organic pigment fine particles of the presentinvention comprises allowing two or more solutions at least one of whichis an organic pigment solution in which an organic pigment is dissolvedto flow through a microchannel in a non-laminar state, and depositingorganic pigment fine particles from the organic pigment solution in thecourse of flowing. By forming such a non-laminar flow in themicrochannel, mixing of solutions is facilitated and thus instantaneousmixing becomes possible, thereby producing nanometer-scale organicpigment fine particles excellent in monodispersibility in a stablemanner.

The term “non-laminar flow” in the present invention means a flow withregular or irregular fluctuation. Generally, when the first viscousfluid (e.g., water) is allowed to flow through a microchannel and a tubenarrower than the microchannel is inserted thereto on the central axisand the second viscous fluid (e.g., colored liquid) is injected thereto,the colored liquid forms a linear stream without fluctuation and flowsin the direction parallel to the channel axis in a stable state when theflow rate is sufficiently low. With gradual increase in the flow rate,the flow becomes unstable and is transformed into a flow withfluctuation. Due to turbulence caused by such fluctuation, the secondviscous fluid is gradually mixed with the first viscous fluid. Types offluctuation include regular fluctuation and irregular fluctuation, andthe present invention encompasses both types.

Flows with regular fluctuation include, for example, flows generatedwhen a columnar object is moved in fluid at an appropriate rate, inwhich opposite vortices (Karman's vortex) are created alternately onboth the right and left sides of the object in the wake flow of theobject under a certain flow condition to form two regular lines; andflows in which a secondary rotating flow (Taylor vortex) is generated byrotation of an inner cylinder with fluid in the circular part of acoaxial double pipe. On the other hand, flows with irregular fluctuationinclude so-called turbulent flow in which vortices of various sizes arerandomly repeatedly formed and broken.

There are various possible factors that produce such regular orirregular fluctuation, such as structures in channels, movement orvibration of walls, external force such as electromagnetic force, andpulsation and kinetic energy of fluid itself. Formation of such anon-laminar flow is effective for mixing two or more kinds of fluidsrapidly and completely. In general, complete mixing refers to a state inwhich molecules constituting two or more fluids are homogeneously mixed.At final stages, they are mixed by molecular diffusion (homogenization).Thus, the key is to increase the contact area of two or more fluids,which is an important parameter for molecular diffusion, in a shortertime. Generally, when viscous fluid flows through a microchannel,viscous force has a greater effect on the fluid than inertial force, andtherefore such increase in the contact area is difficult. However, byutilizing the external or internal force described above to generateflow (convective flow) with regular fluctuation or irregularfluctuation, which is a so-called non-laminar flow, the contact area perunit time is accordingly increased, and rapid complete mixing becomespossible.

REFERENCES

-   1) Kagaku Kogaku Binran 6th ed., The Society of Chemical Engineers,    Japan, Maruzen Co., Ltd.-   2) Rikagaku Jiten 5th ed., Iwanami Shoten Publishers-   3) M. Engler et al., “Effective Mixing by the Use of Convective    Micro Mixers”, Conference Proceedings, 2005 Spring National Meeting,    AIChE, 128d

An example of a microreactor for practicing the method of producingorganic pigment fine particles of the present invention is nowdescribed. The present invention, however, is not limited thereto, andany reactor can be used as long as it is capable of creating anon-laminar flow in a microchannel. Further, solutions for producingorganic pigment fine particles are described below with an example of anorganic pigment solution B and a pH adjustor solution A for changing thepH of the organic pigment solution B.

FIG. 1 illustrates a flat microreactor to which the method of producingorganic pigment fine particles of the present invention is applied.

As shown in FIG. 1, a microreactor 10 is designed so that two dividedsupply channels 12A, 12B branched in the middle of a supply channel 12for supplying a pH adjustor solution A capable of bisecting the solutionA, an undivided supply channel 14 for supplying an organic pigmentsolution B, and a microchannel 16 in which the pH adjustor solution Aand the organic pigment solution B are allowed to react are communicatedat one combining region 18. The divided supply channels 12A, 12B, thesupply channel 14 and the microchannel 16 are positioned onsubstantially the same plane at regular intervals of 90° surrounding thecombining region 18. Specifically, the central axis (dashed line) ofeach channel 12A, 12B, 14, 16 intersects crosswise (intersection angleα=90°) at the combining region 18. Although only the supply channel 12of the pH adjustor solution A whose supply amount is larger than that ofthe organic pigment solution B is divided in FIG. 1, the supply channel14 of the organic pigment solution B may also be divided into severalchannels. The intersection angle α of each channel 12A, 12B, 14, 16disposed around the combining region 18 is not limited to 90° and can beaccordingly determined. The number of division of supply channels 12, 14is not particularly limited, but since the microreactor 10 has acomplicated structure when the number is too large, the division numberis preferably 2 to 10, more preferably 2 to 5.

FIG. 2 illustrates a modification of the flat microreactor 10 in FIG. 1.The intersection angle βbetween the central axis of the supply channel14 and the central axis of divided supply channels 12A, 12B is set to45°, which is smaller than 90° in FIG. 1. The intersection angle αbetween the central axis of the divided supply channels 12A, 12B and thecentral axis of the microchannel 16 is set to 135°.

FIG. 3 illustrates another modification of the flat microreactor 10 inFIG. 1. The intersection angle β between the central axis of the supplychannel 14 through which the organic pigment solution B flows and thecentral axis of the divided supply channels 12A, 12B through which thepH adjustor solution A flows is set to 135°, which is larger than 90° inFIG. 1. The intersection angle α between the central axis of the dividedsupply channels 12A, 12B and the central axis of the microchannel 16 isset to 45°. While the intersection angles α,β relative to the supplychannel 14, divided supply channels 12A, 12B and the microchannel 16 canbe accordingly determined, the angles α, β are preferably determined sothat S1>S2 is satisfied, wherein the sum of the cross sectional areas inthe thickness direction of all of the combined solutions of the organicpigment solution B and the pH adjustor solution A is described as S1 andthe cross sectional area of the microchannel 16 in the radial directionis described as S2. This is because, with this setting, the contact areaof the solutions A, B can be further increased and the length ofdiffusion mixing can be further shortened, and instantaneous mixingoccurs more easily.

FIG. 4 illustrates an example of a three-dimensional microreactor 30 towhich the method of producing organic pigment fine particles of thepresent invention is applied, which is an exploded perspective viewillustrating a three disassembled parts constituting the microreactor30. Parts having the same function as those in FIG. 1 to FIG. 3 aredescribed with the same symbols.

The three-dimensional microreactor 30 is composed of a supply block 32,a combining block 34 and a reaction block 36 which are cylindrical, asmain components. The microreactor 30 is assembled by aligning the sidesof these cylindrical blocks 32, 34, 36 in that order to form a cylinder,and the blocks 32, 34, 36 are integrally fastened using bolts and nuts.

Two annular grooves 38, 40 are concentrically formed on the side face 33of the supply block 32 facing against the combining block 34. When themicroreactor 30 is assembled, two annular grooves 38, 40 each constitutea ring channel through which the organic pigment solution B and the pHadjustor solution A flow. Through holes 42, 44 are each formed so as toreach the outer annular groove 38 and the inner annular groove 40 fromthe opposite side face 35 of the supply block 32 which does not face thecombining block 34. Of the two through holes 42, 44, to the through hole42 communicated to the outer annular groove 38 is connected a supplymeans (a pump, connecting tube, etc.) for supplying the pH adjustorsolution A. A supply means for supplying the organic pigment solution Bis connected to the through hole 44 communicated to the inner annulargroove 40. While the microreactor 30 is configured so that the pHadjustor solution A flows through the outer annular groove 38 and theorganic pigment solution B flows through the inner annular groove 40 inFIG. 4, an opposite configuration is also possible.

A circular combining hole 46 is formed at the center of the side face 41of the combining block 34 facing the reaction block 36. Four long radialgrooves 48, 48 . . . and four short radial grooves 50, 50 . . . areformed alternately and radially from the combining hole 46. Thecombining hole 46 and the radial grooves 48, 50 constitute a circularspace which is the combining region 18 and radial channels through whichthe solutions A, B flow when the microreactor 30 is assembled. Further,through holes 52, 52 . . . are formed at the end of the long radialgrooves 48 of the 8 radial grooves 48, 50 in the thickness direction ofthe combining block 34. These through holes 52 are communicated to theaforementioned outer annular groove 38 formed on the supply block 32.Likewise, through holes 54, 54 . . . are formed at the end of the shortradial grooves 50 in the thickness direction of the combining block 34.These through holes 54 are communicated to the inner annular groove 40formed on the supply block 32.

A through hole 58 communicated to the combining hole 46 is formed at thecenter of the reaction block 36 in the thickness direction. The throughhole 58 corresponds to the microchannel 16.

With these arrangements, the pH adjustor solution A flows through thesupply channel 12 composed of the through hole 42 of the supply block33→the outer annular groove 38→the through holes 52 of the combiningblock 34→the long radial groove 48 to be divided in 4 divided flows, andthe flows reach the combining region 18 (combining hole 46). On theother hand, the organic pigment solution B flows through the supplychannel 14 composed of the through hole 44 of the supply block 32→theinner annular groove 40→the through holes 54 of the combining block34→the short radial grooves 50 to be divided in 4 divided flows, and theflows reach the combining region 18 (combining hole 46). After thedivided flows of the pH adjustor solution A and the divided flows of theorganic pigment solution B are combined at the combining region 18 withmaintaining their kinetic energy, they turn 90° around and flow into themicrochannel 16.

FIG. 5A is a plan view illustrating the combining block 34 and FIG. 5Bis a cross sectional view taken on line a-a in FIG. 5A. In FIG. 5A andFIG. 5B, W represents the width of the divided supply channels 12, 14, Hrepresents the depth of the divided supply channels 12, 14, D representsthe diameter of the combining region 18, and R represents the diameterof the microchannel 16. Generally, the diameter of the combining region18 is the same as the diameter of the microchannel 16. UAin representsthe mean velocity of the pH adjustor solutions A entering into thecombining region 18 flowing through the divided supply channels 12, andUBin is the mean velocity of the organic pigment solutions B enteringinto the combining region 18 flowing through the divided supply channels14. Uout is the mean velocity of the combined solution A, B dischargedfrom the combining region 18 to the microchannel 16.

Preferably, the microchannel 16 is a channel having a length whichprimarily determines flowing characteristics of fluid flowing throughthe channel 16, i.e., a characteristic length, of 1 μm to 1000 μm,preferably 5 μm to 800 μm, more preferably 10 μm to 500 μm in anequivalent diameter. However, when the flow rate is high and the numberof division is large, the channel may have a characteristic length of1000 μm or more because the contact area of solutions can be increasedand the length of diffusion mixing can be shortened. The equivalentdiameter herein described is also called a corresponding diameter, whichis a term used in the field of mechanical engineering. When assuming around tube equivalent to a tube (channel in the present invention) ofany cross section, the diameter of the equivalent round tube is referredto as an equivalent diameter.

The equivalent diameter (deq) is defined as deq=4A/p using A: crosssectional area of a tube and p: wetted perimeter of the tube (peripherallength). When applied to a round tube, the equivalent diametercorresponds to the diameter of the round tube. The equivalent diameteris used for estimating flowing or heat transfer characteristics of atube based on the data of an equivalent round tube and indicates aspatial scale (characteristic length) of a phenomenon. The equivalentdiameter of a square pipe a on a side is deq=4a2/4a=a. The equivalentdiameter of an equilateral triangle a on a side is deq=a/√3. In the caseof a flow between parallel plates with a channel height of h, theequivalent diameter is deq=2h (see, for example, “Encyclopedia ofMechanical Engineering”, The Japan Society of Mechanical Engineers,1997, Maruzen Co., Ltd.).

The microreactors 10, 30 in FIG. 1 to FIG. 4 configured as above can bemanufactured by using processing techniques for precision machines suchas semiconductor processing techniques, especially etching (e.g.,photolithographic etching), ultrafine electric discharge machining,stereo lithography, minor finishing technique and diffused bonding. Inaddition, general machining techniques using a lathe or a drillingmachine may be used.

Materials for the microreactors 10, 30 are not particularly limited aslong as the above-described processing techniques can be applied.Specifically, metal materials (metal such as iron, aluminum, stainlesssteel, titanium), resin materials (fluorine resin, acrylic resin, etc.)and glass (silicon, quartz, etc.) may be used.

The supply means for supplying an organic pigment solution B and a pHadjustor solution A to the microreactors 10, 30 requires a fluid controlfunction for controlling the flow of solutions. Since the behavior offluid in the microchannel 16 has characteristics different from those ina macroscale process, a control system appropriate for a microscaleprocess is necessary. The fluid control system is classified into acontinuous flow system and a liquid droplet (liquid plug) system basedon the formation, and an electric driving system and a pressure drivingsystem based on the driving force.

Of these systems, continuous flow systems are most widely used. In fluidcontrol on the continuous flow system, generally the microchannel 16 iscompletely filled with fluid and the whole fluid is driven by a pressuresource such as a syringe pump provided outside. Although having adisadvantage of a large dead volume, the continuous flow system has agreat advantage that the control system works with a relatively simpleset-up.

A system different from the continuous flow system is a liquid droplet(liquid plug) system. In the system, droplets separated by air areallowed to move inside a reactor or a channel leading to the reactor.The individual droplets are driven by the air pressure. In this process,a vent structure for discharging air between droplets and a channel wallor between droplets to the outside according to need, and a valvestructure for keeping the pressure inside the branched channelindependent of the pressure in other areas needs to be provided in thereactor system. In addition, since operation of droplets is performed bycontrolling pressure difference, a pressure control system composed of apressure source and a switching valve must be constructed outside thereactor. Although the liquid droplet system involves rather complicatedconfiguration and structure of the reactor as described above, sincemulti-stage operation such as individually treating plural portions ofdroplets and sequentially performing several reactions can be done, thedegree of freedom in the system configuration is high.

For the driving system for performing fluid control, an electric drivingsystem in which fluid is moved by an electroosmotic flow generated byapplying high voltage to both ends of the microchannel 16, and apressure driving system in which fluid is moved by applying pressureusing an external pressure source are generally widely used. A knowndifference of the two is that, in terms of the behavior of fluid, whilethe electric driving system has a flat distribution of flow rate profilein the channel cross section, the pressure driving system has ahyperbolic distribution in which the flow rate is high at the center ofthe channel and low at the wall. For transporting fluid whilemaintaining the shape of sample plugs, an electric driving system isbetter suited. The electric driving system inevitably involves acontinuous flow system because the channel needs to be filled withfluid. However, since operation of fluid can be performed by electriccontrol, the system allows a rather complicated process such as creatingtemporal concentration gradient by continuously changing the mixingratio of two solutions. On the other hand, in the case of pressuredriving systems, because control can be done irrespective of electricproperties of fluid and secondary effects such as heat generation orelectrolysis may not be considered, the substrate is substantially notaffected and the system has wide application. However, in view of thefact that an external pressure source must be provided and the responsecharacteristic of operation varies depending on the dead volume in thepressure system, automation of complicated processes is necessary. Thefluid control system used in the present invention is accordinglyselected depending on the intended purpose, but a pressure drivingsystem based on a continuous flow system is preferred.

For controlling the temperature in the microchannel 16 (reactiontemperature control), the temperature may be controlled by putting theentire reactor in a temperature controlled container, or incorporating aheating structure made of metal resistance line or polysilicon into thereactor and performing a thermal cycle using the heating structure forheating while employing natural cooling for cooling. For sensing thetemperature, when a metal resistance line is used, preferably anotherresistance line which is the same as the heater is incorporated and thetemperature is detected based on the variation in the resistance values.When polysilicon is used, the temperature is preferably detected byusing a thermocouple. The channel may also be heated and cooled from theoutside by bringing a Peltier element into contact with the channel.Which method is used is determined depending on the purpose of use orthe material of the channel body.

The number of the microreactors 10,30 used in the present invention maybe one, but plural reactors may be arranged in parallel (numbering-up)to increase the throughput according to need.

The method of producing organic pigment fine particles of the presentinvention using the microreactor 10, 30 configured as above is nowdescribed.

When producing organic pigment fine particles using the microreactor 10,30 in FIG. 1 to FIG. 4 configured as above, organic pigment fineparticles are produced through 3 steps of a dividing step, a combiningstep and a deposition step in any one of the reactors 10,30.

In the dividing step (supply block), at least one solution of the twosolutions A, B of an organic pigment solution B and a pH adjustorsolution A for changing the hydrogen ion exponent of the organic pigmentsolution B is divided into a plurality of solutions.

In the combining step (combining block), solutions are combined so thatthe central axis of at least one divided solution of the plural dividedsolutions and the central axis of the other solution of the twosolutions A, B intersect at one point in the combining region 18.

In the deposition step (reaction block, including the combining hole inthe combining block in some case), organic pigment fine particles aredeposited by changing the hydrogen ion exponent (pH) of the organicpigment solution B by the pH adjustor solution A in the course ofallowing the combined solutions A, B to flow through the microchannel16.

In the microreactor 10 in the FIG. 1 to FIG. 3, the organic pigmentsolution B is divided into two and the pH adjustor solution A is notdivided. In the microreactor 30 in FIG. 4, the organic pigment solutionB and the pH adjustor solution A are each divided into four. Comparingthe organic pigment solution B and the pH adjustor solution A used forproducing organic pigment fine particles, the amount of the pH adjustorsolution A is larger, and so the pH adjustor solution A is preferablydivided.

As described above, at least one solution is divided into a plurality ofsolutions before the organic pigment solution B and the pH adjustorsolution A are combined, and all solutions including the dividedsolutions are combined at the combining region 18. Then, the directionof the combined solutions A, B is changed at a pre-determined angle andthe solutions are allowed to flow through the microchannel 16. As aresult, contraction is generated by the kinetic energy and the change ofdirection of the flow of the combined solutions A, B. Due to increase inthe contact area of the solutions A, B and shortening of the length ofdiffusion mixing, instantaneous mixing can be achieved, and the pH ofthe organic pigment solution B can be instantly brought to the intendedpH in the microchannel 16. Accordingly, nanometer-scale monodisperseorganic pigment fine particles can be produced in a stable manner.

Herein, mixing generally means homogenization of powdery particles,powdery particles and fluid (liquid, gas) or fluid, which contain two ormore components. In particular, fluid containing two or more componentsis desirably homogeneous at a molecular level. Since mixing in themicrochannel 16 occurs basically due to molecular diffusion, to completemixing promptly, the key is to increase the contact area of two or morefluids per unit time. As for the time of instantaneous mixing, the timefrom combining solutions at the combining region to discharging themthrough the microchannel 16 is preferably 1 microsecond to 1000milliseconds, more preferably 10 microseconds to 500 milliseconds.

The method for evaluating mixing of miscible liquids is described, forexample, in Non-patent Document, S. Pani?, et. al, “Experimentalapproaches to a better understanding of mixing performance ofmicrofluidic devices”, Chem. Eng. J. 101, 2004, p. 409-p. 419. Themixing time can be calculated from values obtained by dividing thevolume (mL) of a microchannel 16 in which mixing occurs by the totalflow in the channel (mL/second) under conditions where mixing isconsidered to be completed according to the aforementioned mixingevaluation method.

Principles and methods of mixing in the microchannel 16 are described indetail, for example, in Non-patent Document V. Hessel, et. al.,“Chemical Micro Process Enginnering-Processing and Plant-” WILEY-VCH,2005, p. 1-p. 280.

To form a non-laminar flow in the microchannel 16 in the production oforganic pigment fine particles, the shear rate (1/second) represented byU/R in which R(m) represents the equivalent diameter of the microchannel16 and U (m/second) represents the mean velocity of a solution flowingthrough the microchannel 16 is preferably set to 100 or more.

FIG. 6 shows analysis of the relation between the shear rate (U/R) andthe mixing ability in the microchannel 16 described in Non-patentDocument 4. The mixing ability is evaluated based on the turbidity ofthe solution represented by the absorbance. Specifically, the higher theabsorbance, the poor the mixing ability, and the lower the absorbance,the better the mixing ability. As can be shown in FIG. 6, with increasein the shear rate (U/R) in the microchannel 16, the absorbance israpidly decreased, and remains substantially the same at (U/R) of 100 ormore. This implies that mixing different from mixing by moleculardiffusion in a laminar flow, i.e., mixing by molecular diffusion in anon-laminar flow is occurring in the zone where the shear rate (U/R) is100 or more. By designing an appropriate relation between the equivalentdiameter R(m) of the microchannel 16 and the mean velocity U (m/second)of a solution flowing through the microchannel 16, the shear rate (U/R)in the microchannel 16 can be 100 or more. As a result, instantaneousmixing can be performed. Although the graph of FIG. 6 does not showdetailed behavior of the mixing ability when the shear rate (U/R) is 100or more, upon examination of particle size of organic pigment fineparticles produced at a high shear rate range of about 20,000 (1/second)to 100,000 (1/second) in Example 3 described later, the higher the shearrate, the smaller the particle size even in such a high shear raterange. From this, it is considered that the higher the shear rate, themore the mixing ability is improved, even if the shear rate is higherthan 100 (1/second).

To form a contraction by the change of the direction of solutions A, Bat the combining region 18, such a construction can be formed byappropriately designing the relation between the mean velocity of thesolutions A, B upon combining and the intersection angles α, β of thecentral axes of the solutions A, B upon combining. Further, rapid changein the direction of the solutions A, B at the combining region 18 makesit easier to form a flow with regular or irregular fluctuation. It isconsidered that by establishing an appropriate relation between the meanvelocity of the solutions A, B flowing into the combining region 18 andthe intersection angles α, β of the central axes of the solutions A, Bupon combining, a non-laminar flow is easily formed in the microchannel16.

The temperature of the solutions A, B flowing through the microchannel16 may be within the range that the aqueous medium does not coagulate orboil, and is preferably −20° C. to 90° C., more preferably −10° C. to50° C., particularly preferably 0 to 30° C. The flow rate of thesolutions A, B flowing through the microchannel 16 is also preferably0.1 to 5000 mL/minute, more preferably 1 to 1000 mL/minute, particularlypreferably 5 to 500 mL/minute. In the present invention, the range ofthe concentration of substrate (organic pigment and a reactant thereof)flowing through the microchannel 16 is generally 0.5 to 20% by mass,preferably 1.0 to 10% by mass.

The hue of the organic pigment used in the present invention is notlimited. A magenta pigment, a yellow pigment or a cyan pigment may beused. Specifically, a magenta pigment, a yellow pigment or a cyanpigment such as perylene, perinone, quinacridone, quinacridonquinone,anthraquinone, anthanthrone, benzimidazolone, disazo condensation,disazo, azo, indanthrone, phthalocyanine, triarylcarbonium, dioxazine,aminoanthraquinone, diketopyrrolopyrrole, thioindigo, isoindoline,isoindolinone, pyranthrone or isoviolanthrone pigment or a mixturethereof may be used. More specifically, useful are a perylene pigmentsuch as C.I. pigment red 190 (C.I.No. 71140), C.I. pigment red 224(C.I.No. 71127) or C.I. pigment violet 29 (C.I.No. 71129), a perinonepigment such as C.I. pigment orange 43 (C.I.No. 71105) or C.I. pigmentred 194 (C.I.No. 71100), a quinacridone pigment such as C.I. pigmentviolet 19 (C.I.No. 73900), C.I. pigment violet 42, C.I. pigment red 122(C.I.No. 73915), C.I. pigment red 192, C.I. pigment red 202 (C.I.No.73907), C.I. pigment red 207 (C.I.No. 73900, 73906) or C.I. pigment red209 (C.I.No. 73905), a quinacridonequinone pigment such as C.I. pigmentred 206 (C.I.No. 73900/73920), C.I. pigment orange 48 (C.I.No.73900/73920) or C.I. pigment orange 49 (C.I.No. 73900/73920), ananthraquinone pigment such as C.I. pigment yellow 147 (C.I.No. 60645),an anthanthrone pigment such as C.I. pigment red 168 (C.I.No. 59300), abenzimidazolone pigment such as C.I. pigment brown 25 (C.I.No. 12510),C.I. pigment violet 32 (C.I.No. 12517), C.I. pigment yellow 180 (C.I.No.21290), C.I. pigment yellow 181 (C.I.No. 11777), C.I. pigment orange 62(C.I.No. 11775) or C.I. pigment red 185 (C.I.No. 12516), a disazocondensation pigment such as C.I. pigment yellow 93 (C.I.No. 20710),C.I. pigment yellow 94 (C.I.No. 20038), C.I. pigment yellow 95 (C.I.No.20034), C.I. pigment yellow 128 (C.I.No. 20037), C.I. pigment yellow 166(C.I.No. 20035), C.I. pigment orange 34 (C.I.No. 21115), C.I. pigmentorange 13 (C.I. No. 21110), C.I. pigment orange 31 (C.I. No. 20050),C.I. pigment red 144 (C.I.No. 20735), C.I. pigment red 166 (C.I.No.20730), C.I. pigment red 220 (C.I. No. 20055), C.I. pigment red 221(C.I.No. 20065), C.I. pigment red 242 (C.I.No. 20067), C.I. pigment red248, C.I. pigment red 262 or C.I. pigment brown 23 (C.I.No. 20060), adisazo pigment such as C.I. pigment yellow 13 (C.I.No. 21100), C.I.pigment yellow 83 (C.I.No. 21108) or C.I. pigment yellow 188 (C.I.No.21094), an azo pigment such as C.I. pigment red 187 (C.I.No. 12486),C.I. pigment red 170 (C.I.No. 12475), C.I. pigment yellow 74 (C.I.No.11714), C.I. pigment red 48 (C.I.No. 15865), C.I. pigment red 53(C.I.No. 15585), C.I. pigment orange 64 (C.I.No. 12760) or C.I. pigmentred 247 (C.I.No. 15915), an indanthrone pigment such as C.I. pigmentblue 60 (C.I.No. 69800), a phthalocyanine pigment such as C.I. pigmentgreen 7 (C.I.No. 74260), C.I. pigment green 36 (C.I.No. 74265), pigmentgreen 37 (C.I.No. 74255), pigment blue 16 (C.I.No. 74100), C.I. pigmentblue 75 (C.I.No. 74160:2) or 15 (C.I.No. 74160), a triarylcarboniumpigment such as C.I. pigment blue 56 (C.I.No. 42800) or C.I. pigmentblue 61 (C.I.No. 42765;1), a dioxazine pigment such as C.I. pigmentviolet 23 (C.I.No. 51319) or C.I. pigment violet 37 (C.I.No. 51345), anaminoanthraquinone pigment such as C.I. pigment red 177 (C.I.No. 65300),a diketopyrrolopyrrole pigment such as C.I. pigment red 254 (C.I. No.56110), C.I. pigment red 255 (C.I.No. 561050), C.I. pigment red 264,C.I. pigment red 272 (C.I.No. 561150), C.I. pigment orange 71 or C.I.pigment orange 73, a thioindigo pigment such as C.I. pigment red 88(C.I.No. 73312), an isoindoline pigment such as C.I. pigment yellow 139(C.I.No. 56298) or C.I. pigment orange 66 (C.I.No. 48210), anisoindolinone pigment such as C.I. pigment yellow 109 (C.I. No. 56284)or a C.I. pigment orange 61 (C.I.No. 11295), a pyranthrone pigment suchas C.I. pigment orange 40 (C.I. No. 59700) or C.I. pigment red 216(C.I.No. 59710), and an isoviolanthrone pigment such as C.I. pigmentviolet 31 (60010).

A preferred pigment is a quinacridone, diketopyrrolopyrrole, disazocondensation, azo or phthalocyanine pigment. A particularly preferredpigment is a quinacridone, disazo condensation, azo or phthalocyaninepigment.

In the present invention, two or more organic pigments, a solid solutionof an organic pigment or combination of an organic pigment and aninorganic pigment may also be used. Such an organic pigment needs to behomogeneously dissolved in an alkaline or acidic aqueous medium. Whetherthe pigment is dissolved in an acidic medium or an alkaline medium isdetermined based on under which condition the pigment can be easilyhomogeneously dissolved. Generally, for pigments containing, in theirmolecule, a group which can be dissociated under an alkali condition, analkaline aqueous medium is used. For pigments which does not contain agroup which can be dissociated under an alkaline condition and containsa large number of nitrogen atoms to which proton can be easily attached,an acidic aqueous medium is used. For example, quinacridone,diketopyrrolopyrrole and disazo condensation pigments are dissolved inan alkaline aqueous medium and phthalocyanine pigments are dissolved inan acidic aqueous medium.

The base used for dissolving a pigment in an alkaline aqueous mediumincludes an inorganic base such as sodium hydroxide, calcium hydroxideor barium hydroxide, or an organic base such as trialkylamine,diazabicycloundecene (DBU) or metal alkoxide. Preferably, the base is aninorganic base. The amount of the base to be used is not particularlylimited as long as the pigment can be homogeneously dissolved in themedium. An inorganic base is used in a proportion of preferably 1.0 to30 molar equivalents, more preferably 2.0 to 25 molar equivalents,further preferably 3 to 20 molar equivalents based on the amount of thepigment. An organic base is used in a proportion of preferably 1.0 to100 molar equivalents, more preferably 5.0 to 100 molar equivalents, andfurther preferably 20 to 100 molar equivalents based on the amount ofthe pigment.

The acid used for dissolving a pigment in an acidic aqueous mediumincludes an inorganic acid such as sulfuric acid, hydrochloric acid orphosphoric acid, or an organic acid such as acetic acid, trifluoroaceticacid, oxalic acid, methanesulfonic acid or trifluoromethanesulfonicacid. The acid is preferably an inorganic acid, particularly preferablysulfuric acid. The amount of the acid to be used is not particularlylimited as long as the pigment can be homogeneously dissolved in themedium, but the acid is used in an excess amount compared to the amountof the base. Irrespective of whether it is inorganic or organic, theacid is used in a proportion of preferably 3 to 500 molar equivalents,more preferably 10 to 500 molar equivalents, further preferably 30 to200 molar equivalents based on the amount of the pigment.

The aqueous medium is now described. The aqueous medium in the presentinvention is a medium in which a pigment is dissolved with an alkali oran acid, and which is soluble in water. The aqueous medium means wateralone or an organic solvent soluble in water. Examples of organicsolvents soluble in water include a monohydric alcohol solvent which istypically methanol, ethanol, isopropanol or t-butanol, a polyhydricalcohol solvent which is typically ethylene glycol, propylene glycol,diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol,2-methyl-1,3-propanediol, 1,2,6-hexanetriol, acetylene glycolderivatives, glycerol or trimethylolpropane, a lower monoalkyl ethersolvent of polyhydric alcohol such as ethylene glycol monomethyl(orethyl)ether, diethylene glycol monomethyl(or ethyl)ether or triethyleneglycol monoethyl(or butyl)ether, a polyether solvent such as ethyleneglycol dimethyl ether (monoglyme), diethylene glycol dimethyl ether(diglyme) or triethylene glycol dimethyl ether (triglyme), an amidesolvent such as dimethylformamide, dimethylacetamide, 2-pyrrolidone,N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, urea ortetramethylurea, a sulfur-containing solvent such as sulfolane, dimethylsulfoxide or 3-sulfolene, a polyfunctional solvent such as diacetonealcohol or diethanolamine, a carboxylic acid solvent such as aceticacid, maleic acid, docosahexaenoic acid, trichloroacetic acid ortrifluoroacetic acid, and a sulfonic acid solvent such asmethanesulfonic acid or trifluorosulfonic acid. These solvents may beused in a mixture of two or more. A preferred organic solvent is anamide solvent or a sulfur-containing solvent as an alkaline solvent, anda carboxylic acid solvent, a sulfur solvent or a sulfonic acid solventas an acidic solvent. A more preferred organic solvent is asulfur-containing solvent as an alkaline solvent and a sulfonic acidsolvent as an acidic solvent. A particularly preferred solvent isdimethyl sulfoxide (DMSO) as an alkaline solvent and methanesulfonicacid as an acidic solvent.

When using a mixed solvent of water and an organic solvent as an aqueousmedium, the mixing ratio of water and the organic solvent is notparticularly limited as long as a pigment can be homogeneously dissolvedtherein. Preferably, the mixing ratio is water/organic solvent=0.05 to10 (mass ratio) for an alkaline solvent. When the solvent is acidic andan inorganic acid is used, no organic solvent is used. Preferably, forexample, sulfuric acid alone is used. When an organic acid is used, theorganic acid itself acts as an organic solvent. To adjust the viscosityand the solubility, a plurality of acids may be mixed, or water may beadded thereto. Preferably, the mixing ratio is water/organic solvent(organic acid)=0.005 to 0.1 (mass ratio).

In the present invention, preferably a solution in which a pigment ishomogeneously dissolved is introduced into a channel. When a suspensionis introduced into a channel, fine particles may have an increasedparticle size and a broad particle size distribution, and channels areeasily blocked in some cases. The expression “homogeneously dissolved”refers to a solution which has substantially no turbidity when observedwith visible light. In the present invention, a solution obtained byfiltering through a micro-filter of 1 μm or less, or a solution whichdoes not contain substances left when filtered through a micro-filter of1 μm is defined as a “homogeneously dissolved” solution.

The hydrogen ion exponent (pH) is now described. The hydrogen ionexponent (pH) is a common logarithm of the reciprocal of hydrogen ionconcentration (molar concentration), which is also referred to ashydrogen exponent. The hydrogen ion concentration means theconcentration of hydrogen ions H+ in a solution, indicating the molarnumber of hydrogen ions present in 1 L of a solution. Since the hydrogenion concentration fluctuates in an extremely wide range, theconcentration is generally expressed by the hydrogen ion exponent (pH).For example, pure water contains 10⁻⁷ moles of hydrogen ions at 1 atm at25° C., and so pure water has pH of 7 and is neutral. An aqueoussolution with pH <7 is acidic, and an aqueous solution with pH >7 isalkaline. Methods of measuring pH include potentiometry and colorimetry.

The present invention, particularly claim 2, provides a method ofproducing organic pigment fine particles, comprising changing thehydrogen ion exponent (pH) in the course of flowing through themicrochannel 16. The method is performed using a channel having anotherfeed port different from a feed port of a homogeneous solution oforganic pigment, for example, a channel having at least two feed portsshown in FIG. 1. Specifically, a homogeneous organic pigment solution isintroduced through a feed port in FIG. 1, and neutral, acidic oralkaline water or an aqueous solution in which a dispersant is dissolvedin such water is introduced through another feed port in FIG. 1. Then,the solutions are brought into contact with each other at a combiningregion 18 and in the microchannel 16, thereby bringing the hydrogen ionconcentration, i.e., the hydrogen ion exponent (pH) of the solutioncontaining organic pigment, closer to neutral (pH 7). Since pigment isdifficult to be dissolved in an aqueous medium under a low alkaline or alow acidic condition, fine particles of the pigment are deposited as thehydrogen ion exponent (pH) of the solution containing the organicpigment approaches neutral, and the deposited fine particles aredelivered through a discharge port of the microchannel 16.

The change in the hydrogen ion exponent (pH) when producing pigment fineparticles from a pigment dissolved in an alkaline aqueous medium isgenerally within pH 16.0 to 5.0, preferably within pH 16.0 to 10.0. Thechange in the hydrogen ion exponent (pH) when producing pigment fineparticles from a pigment dissolved in an acidic aqueous medium isgenerally within pH 1.5 to 9.0, preferably within pH 1.5 to 4.0. Whilethe range of the change depends on the hydrogen ion exponent (pH) of theorganic pigment solution, a range sufficient for allowing the organicpigment to deposit may be used.

The dispersant added to the solution is now described. In the method ofproducing organic pigment fine particles of the present invention, adispersant may be added to an organic pigment solution B containing anorganic pigment and/or a pH adjustor solution A for changing thehydrogen ion exponent (pH). The dispersant rapidly adsorbs to thesurface of deposited pigment to form fine pigment particles and has afunction to prevent the fine particles from coagulating. In the presentinvention, for such a dispersant, an anionic, cationic, amphoteric,nonionic or pigment-type low molecular weight or high molecular weightdispersant may be used. These dispersants may be used alone or incombination. The dispersant used for dispersing a pigment is describedin detail in “Stabilization of Pigment Dispersion and Surface TreatmentTechnique/Evaluation” (Japan Association for International ChemicalInformation, December, 2001) pp. 29 to 46.

Examples of anionic dispersants (anionic surfactants) includeN-acyl-N-alkyltaurine salts, fatty acid salts, alkylsulfates,alkylbenzenesulfonates, alkylnaphthalenesulfonates,dialkylsulfosuccinates, alkylphosphates, naphthalenesulfonic acidformalin condensates and polyoxyethylene alkylsulfates. Of these,N-acyl-N-alkyltaurine salts are preferred. N-acyl-N-alkyltaurine saltsdescribed in Japanese Patent Application Laid-Open No. 3-273067 arepreferred. These anionic dispersants may be used alone or in combinationof two or more.

Examples of cationic dispersants (cationic surfactants) includequaternary ammonium salts, alkoxylated polyamines, aliphatic aminepolyglycol ethers, aliphatic amines, diamines and polyamines derivedfrom aliphatic amine and aliphatic alcohol, imidazoline derived fromfatty acid, and salts of these cationic substances. These cationicdispersants may be used alone or in combination of two or more.

An amphoteric dispersant has in its molecule both an anionic groupmoiety which the aforementioned anionic dispersant has in its moleculeand a cationic group moiety which the aforementioned cationic dispersanthas in its molecule.

Examples of nonionic dispersants (nonionic surfactants) includepolyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers,polyoxyethylene fatty acid esters, sorbitan fatty acid esters,polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkylaminesand glycerol fatty acid esters. Of these, polyoxyethylene alkylarylethers are preferred. These nonionic dispersants may be used alone or incombination of two or more.

A pigment dispersant is defined as a dispersant derived from an organicpigment as a parent material, which is produced by chemical modificationof the parent structure. Examples thereof include sugar-containingpigment dispersants, piperidyl-containing pigment dispersants, pigmentdispersants derived from naphthalene or perylene, pigment dispersantscontaining a functional group linked to a pigment parent structurethrough a methylene group, pigment dispersants containing a pigmentparent structure chemically modified by polymer, pigment dispersantscontaining a sulfonic group, pigment dispersants containing asulfonamide group, pigment dispersants containing an ether group, andpigment dispersants containing a carboxylic acid group, a carboxylicacid ester group or a carboxamide group.

Specific examples of high molecular weight dispersants includepolyvinylpyrrolidone, polyvinyl alcohol, polyvinyl methyl ether,polyethylene oxide, polyethylene glycol, polypropylene glycol,polyacrylamide, vinyl alcohol-vinyl acetate copolymers, partiallyformalized polyvinyl alcohol, partially butyralized polyvinyl alcohol,vinylpyrrolidone-vinyl acetate copolymers, polyethylene oxide/propyleneoxide block copolymers, polyacrylic acid salts, polyvinylsulfuric acidsalts, poly(4-vinylpiridine) salts, polyamides, polyallylamine salts,condensed naphthalenesulfonic acid salts, styrene-acrylic acid saltcopolymers, styrene-methacrylic acid salt copolymers, acrylicester-acrylic acid salt copolymers, acrylic ester-methacrylic acid saltcopolymers, methacrylic ester-acrylic acid salt copolymers, methacrylicester-methacrylic acid salt copolymers, styrene-itaconic acid saltcopolymers, itaconic acid ester-itaconic acid salt copolymers,vinylnaphthalene-acrylic acid salt copolymers,vinylnaphthalene-methacrylic acid salt copolymers,vinylnaphthalene-itaconic acid salt copolymers, cellulose derivativesand starch derivatives. In addition, natural polymers such as alginate,gelatin, albumin, casein, gum arabic, tragacanth gum and ligninsulfonicacid salts may also be used. Of these, polyvinylpyrrolidone ispreferred. These polymers may be used alone or in combination of two ormore.

The amount of dispersant to be added is preferably 0.1 to 1000 parts bymass, more preferably 1 to 500 parts by mass, further preferably 10 to250 parts by mass based on 100 parts by mass of the pigment to furtherimprove the uniform dispersibility and the storage stability of thepigment. When the amount is less than 0.1 parts by mass, the dispersionstability of organic pigment fine particles may not be improved.

The method of measuring the particle size of the produced organicpigment fine particles is now described. In the methods of measuringfine particles, there are approaches to express an average size in agroup of particles in numerical values. Typically used are modediameters which show the maximum value in a particle size distribution,median diameters which correspond to the central value in an integraldistribution curve and various average diameters (length average, areaaverage, weight average). The particle size of the organic pigment fineparticles produced by the method of the present invention is optional aslong as the microchannel 16 is not blocked. The organic pigment fineparticles have a mode diameter of preferably 1 μm or less, morepreferably 3 nm to 800 nm, particularly preferably 5 nm to 500 nm.

The size and size distribution of the produced organic pigment fineparticles are now described.

Uniformity in particle size of fine particles, i.e., monodispersibilityof fine particles, means that not only the contained particles have auniform size but also there is no variation in the chemical compositionand the crystal structure of the particles, and so such uniformity is animportant factor for determining ability of particles. In particular,such monodispersibility is considered an important factor forcontrolling properties of fine particles with a particle size of ananometer level. The method of the present invention is excellent inthat not only it can control particle size but also it can make theparticle size uniform. As an index of uniformity in particle size,arithmetic standard deviation is used. The organic pigment fineparticles produced by the present invention have an arithmetic standarddeviation of preferably 130 nm or less, particularly preferably 80 nm orless. The arithmetic standard deviation is an approach to calculate thestandard deviation assuming a particle size distribution to be a normaldistribution, and is obtained by subtracting the 16% particle size fromthe 84% particle size in the integrated distribution, and dividing thedifference by 2.

EXAMPLES

The present invention will be described in more detail with reference tothe following Examples, but these Examples are not intended to limit thepresent invention in any way.

Example 1

In Example 1, organic pigment fine particles of Pigment Red 122 (C. I.No. 73915) were produced.

A pH was measured by pH meter F-54 (measurement range pH 0 to 14) fromHORIBA, Ltd. A particle size distribution of the produced organicpigment fine particles was measured by Nanotrac UPA-EX 150 from NIKKISOCO., LTD.

An organic pigment solution B and a pH adjustor solution A were preparedas follows:

(1) Organic pigment solution B

-   -   2,9-Dimethylquinacridone . . . 7.5 g    -   Dispersant polyvinylpyrrolidone (from Wako Pure Chemical        Industries, Ltd., K30) . . . 37.5 g    -   Aqueous solution of 0.8 M potassium hydroxide . . . 83 mL    -   Dimethylsulfoxide (DMSO) . . . 568 mL

The above components were sufficiently mixed under stirring anddissolved completely at room temperature. Then, this solution was passedthrough a 0.45 μm microfilter to remove impurities such as debris. ThepH of the organic pigment solution thus prepared exceeded themeasurement limit (pH 14), and therefore unmeasurable.

(2) pH adjustor solution A

-   -   Dispersant oleylmethyl taurine sodium salt . . . 75 g    -   Distilled water . . . 9,000 g

The above components were sufficiently mixed under stirring anddissolved completely at room temperature. Then, this solution was passedthrough a 0.45 μM microfilter to remove impurities such as debris. ThepH of the pH adjustor solution A thus prepared was 7.7.

(3) A three-dimensional microreactor shown in FIG. 4, which has thefollowing number of division (number of channels) was used as amicroreactor.i) Number of supply channels (n) . . . The organic pigment solution Bwas divided into 5, and the pH adjustor solution A was divided into 5.ii) Width of supply channels 12, 14 (W) . . . 100 μm eachiii) Height of supply channels 12, 14 (H) . . . 100 μm eachiv) Diameter of a combining region 18 (D) . . . 320v) Diameter of a microchannel 16 (R) . . . 360 μmvi) Inlet and outlet areas . . . The total inlet area (S1) was 0.1 mm²and the outlet area (S2) was 0.1 mm² so that they were the same.vii) Intersection angle of the central axes between each of supplychannels 12, 14 and a microchannel 16 at a combining region 18 . . . 90°viii) Material for a microreactor . . . Stainless (SUS304)ix) Channel processing method . . . Performed by microelectric dischargemachining, and 3 parts: a supply block 32, a combining block 34, and areaction block 36 were sealed by metal surface sealing with metalgrinding.(4) Reaction conditionsi) Predetermined flow rate . . . Using a syringe pump (from HarvardCo.), the organic pigment solution B and the pH adjustor solution A weresupplied at constant flow rates 2.867 mL/minute and 17.146 mL/minute,respectively. The flow rate of a dispersion of organic pigment fineparticles flowing in a microchannel 16 was about 20 mL/minute, and aflow rate ratio between the organic pigment solution B and the pHadjustor solution A was 1:6.ii) Average flow rate of solutions A, B . . . UBin was 0.956 m/second,UAin was 5.715 m/second, and Uout was 3.275 m/second.iii) Shear rate . . . Shear rate in a microchannel 16 (U/R)=9.0×10³iv) Reaction temperature . . . 10° C.(5) Production results

i) Particle Size and Particle Size Distribution Results

The median average size M 50% of organic pigment fine particles producedin Example 1 under the aforementioned conditions was 9.2 nm (volumeaverage size Mv=10.1 nm, number average size Mn=7.8 nm), and thearithmetic standard deviation STD was 3.3 nm (see FIG. 7). Asappreciated from the above results, organic pigment fine particles in ananometer size, excellent in monodispersibility could be stably producedin Example 1.

Moreover, stable continuous production was able to be performed withoutcausing blocking during production. In the case of calculation based onoperation of 6,000 hours per year, one microreactor produces 7.2tons/year, which is a high throughput usable in real production.Pressure loss through a microreactor is 0.16 MPa, and thereforeoperation with low pressure loss can be performed. Desired organicpigment fine particles could be obtained with low power.

Comparative Example 1

Organic pigment fine particles were produced using solutions A, B thesame as those in Example 1 as well as a 50 mL small-size container withstirrer (in a form of tank).

(1) Reaction Conditions

The aforementioned small-size container was immersed into a thermostattank kept the temperature at 10° C. To the container, 6 mL of a pHadjustor solution was added, and the mixture was stirred at a revolvingspeed of 500 rpm. During the stirring, 1 mL of an organic pigmentsolution was added from the liquid surface at an addition speed of 1mL/minute using a syringe pump (from Harvard Co.).

(2) Production Results i) Particle Size and Particle Size DistributionResults

The median average size M 50% of the organic pigment fine particlesproduced in Comparative Example 1 under the aforementioned conditionswas 14.1 nm (volume average size Mv=16.9 nm, number average size Mn=10.5nm), and the arithmetic standard deviation STD was 7.7 nm, which resultswere worse than those of Example 1.

Example 2

In Example 2, organic pigment fine particles of Pigment Yellow 128 (C.I. No. 20037) were produced.

The particle size distribution of Example 2 was measured by a dynamiclight scattering particle size distribution meter (LB-550) from HORIBA,Ltd.

(1) Organic pigment solution B

-   -   Pigment (P. Y. 128) . . . 1.25 g    -   Dispersant polyvinylpyrrolidone (from Wako Pure Chemical        Industries, Ltd., K30) . . . 1.25 g    -   Aqueous solution of 1 M potassium hydroxide . . . 6.0 mL    -   Dimethylsulfoxide (DMSO) . . . 82 mL

The above components were sufficiently mixed under stirring anddissolved completely at room temperature. This solution was clear andyellow-brown. Then, this solution was passed through a 0.45 μmmicrofilter to remove impurities such as debris.

(2) pH adjustor solution A

-   -   Dispersant oleylmethyl taurine sodium salt . . . 10 g    -   Distilled water . . . 990 g

The above components were sufficiently mixed under stirring anddissolved completely at room temperature. Then, this solution was passedthrough a 0.45 μM microfilter to remove impurities such as debris.

(3) A three-dimensional microreactor shown in FIG. 4, which has thefollowing number of division (number of channels) was used as amicroreactor.i) Number of supply channels (n) . . . The organic pigment solution Bwas divided into 7, and the pH adjustor solution A was divided into 7.ii) Width of supply channels 12, 14 (W) . . . 50 μm eachiii) Height of supply channels 12, 14 (H) . . . 50 μm eachiv) Diameter of a combining region 18 (D) . . . 220 μmv) Diameter of a microchannel 16 (R) . . . 200 μmvi) Inlet and outlet areas . . . The total inlet area (S1) was 0.035 mm²and the outlet area (S2) was 0.031 mm² so that they were different fromeach other.vii) Intersection angle of the central axes between supply channels 12,14 and a microchannel 16 at a combining region 18 . . . 90°viii) Material for a microreactor . . . Stainless (SUS304)ix) Channel processing method . . . Performed by microelectric dischargemachining, and 3 parts: a supply block 32, a combining block 34, and areaction block 36 were sealed by metal surface sealing with metalgrinding.(4) Reaction conditionsi) Predetermined flow rate . . . Using a syringe pump (from HarvardCo.), the organic pigment solution B and the pH adjustor solution A weresupplied at constant flow rates 3 mL/minute and 12 mL/minute,respectively. The flow rate of a dispersion of organic pigment fineparticles flowing in a microchannel 16 was about 15 mL/minute, and aflow rate ratio between the organic pigment solution B and the pHadjustor solution A was 1:4.ii) Average flow rate of solutions A, B . . . UBin was 2.857 m/secondand UAin was 11.429 m/second, and Uout was 7.958 m/second.iii) Shear rate . . . Shear rate in a microchannel (U/R)=4.0×10⁴iv) Reaction temperature . . . 20° C.(5) Production results

i) Particle Size and Particle Size Distribution Results

The median average size M 50% of the organic pigment fine particlesproduced in Example 2 under the aforementioned conditions was 21.1 nm,and the arithmetic standard deviation STD was 5.5 nm. As appreciatedfrom the above results, organic pigment fine particles in a nanometersize, excellent in monodispersibility could be stably produced inExample 2 (see FIG. 8). Moreover, stable continuous production was ableto be performed without causing blocking during production.

Comparative Example 2

Organic pigment fine particles were produced using solutions A, B thesame as those in Example 2 as well as a 50 mL small-size container withstirrer (in a form of tank).

(1) Reaction Conditions

The aforementioned small-size container was immersed into a thermostattank kept the temperature at 20° C. To the container, 12 mL of a pHadjustor solution A was added, and the mixture was stirred at arevolving speed of 500 rpm. During the stirring, 3 mL of an organicpigment solution B was added from the liquid surface at an additionspeed of 3 mL/minute using a syringe pump (from Harvard Co.).

(2) Production Results i) Particle Size and Particle Size DistributionResults

The median average size M 50% of the organic pigment fine particlesproduced in Comparative Example 1 under the aforementioned conditionswas 47.4 nm, and the arithmetic standard deviation STD was 33.8 nm,which results were worse than those of Example 2 (see FIG. 8).

Example 3

In Example 3, changes of a particle size of produced organic pigmentfine particles (Pigment Yellow 74 (C. I. No. 11714)) by changing a shearrate (U/R) in a microchannel 16 were tested.

The particle size distribution of Example 3 was measured by a dynamiclight scattering particle size distribution meter (LB-550) from HORIBA,Ltd.

(1) Organic pigment solution B

-   -   Pigment (P. Y. 74) . . . 1.2 g    -   Dispersant polyvinylpyrrolidone (from Wako Pure Chemical        Industries, Ltd., K30) . . . 6.0 g    -   Aqueous solution of 1 M potassium hydroxide . . . 3.8 mL    -   Dimethylsulfoxide (DMSO) . . . 109 mL

The above components were sufficiently mixed under stirring anddissolved completely at room temperature. This solution was red-brown.Then, this solution was passed through a 0.45 μm microfilter to removeimpurities such as debris.

(2) pH adjustor solution A

-   -   Dispersant oleylmethyl taurine sodium salt . . . 10 g    -   Distilled water . . . 990 g

The above components were sufficiently mixed under stirring anddissolved completely at room temperature. Then, this solution was passedthrough a 0.45 microfilter to remove impurities such as debris.

(3) The used microreactor was the same as that of Example 2.(4) Reaction conditionsi) Predetermined flow rate . . . Using a syringe pump (from HarvardCo.), the organic pigment solution B and the pH adjustor solution A weresupplied at a constant flow rate under the shear rate conditions listedfor Test 1 to Test 4 in Table 1. The flow rate ratio of a dispersion oforganic pigment fine particles flowing in the microchannel 16 is 1:8.ii) Reaction temperature . . . 20° C.

TABLE 1 Organic pigment pH adjuster Median Shear rate solution solutionShear rate average conditions (ml/min) (ml/min) (l/second) size (nm)Test 1 1 8 2.4 × 10⁴ 84.3 Test 2 2 16 4.8 × 10⁴ 64.7 Test 3 3 24 7.2 ×10⁴ 61.1 Test 4 4 32 9.5 × 10⁴ 53.6(5) Test results

The test results are shown in Table 1 and FIG. 9. As appreciated fromTable 1 and FIG. 9, as the shear rate in the microchannel 16 becomeshigher, the median average size of the produced organic pigment fineparticles gradually become smaller. This means that the particle size ofthe organic pigment fine particle to be produced can be controlled bychanging the shear rate in the microchannel 16.

1. A method of producing organic pigment fine particles, includingallowing two or more solutions at least one of which is an organicpigment solution in which an organic pigment is dissolved to flowthrough a microchannel, and depositing organic pigment fine particlesfrom the organic pigment solution in a course of flowing, the methodcomprising: the step of dividing at least one solution of two or moresolutions comprising the organic pigment solution in which an organicpigment is dissolved in an alkaline or acidic aqueous medium and a pHadjustor solution for changing a hydrogen ion exponent of (pH) theorganic pigment solution into a plurality of solutions; the step ofcombining solutions so that a central axis of at least one dividedsolution of the plural divided solutions and the central axis of anothersolution of the two or more solutions different from the one dividedsolution intersect at one point in a combining region; and the step ofdepositing the organic pigment fine particles by changing the hydrogenion exponent (pH) of the organic pigment solution by the pH adjustorsolution in the course of allowing the combined solutions to flowthrough the microchannel.
 2. The method of producing organic pigmentfine particles according to claim 1, wherein the two or more solutionsare allowed to flow through the microchannel in a non-laminar state. 3.The method of producing organic pigment fine particles according toclaim 1, wherein in the step of combining, an intersection angle of thecentral axes upon combining the solutions is determined so that S1>S2 issatisfied, wherein a sum of the cross sectional areas of all of thecombined solutions in the thickness direction is described as S1 and thecross sectional area of the microchannel in the radial direction isdescribed as S2, and thereby contracting the flow of the solutions atthe combining region.
 4. The method of producing organic pigment fineparticles according to claim 1, wherein a time of mixing the solutionsfrom being combined at the combining region and discharged through themicrochannel is 1 microsecond to 1000 milliseconds.
 5. The method ofproducing organic pigment fine particles according to claim 1, whereinthe microchannel has a characteristic length in an equivalent diameterof 1 μm to 1000 μm.
 6. The method of producing organic pigment fineparticles according to claim 1, further comprising changing a shear rate(1/second) represented by U/R, wherein the equivalent diameter of themicrochannel is described as R(m) and a mean velocity of a solutionflowing through the microchannel is described as U (m/second).
 7. Themethod of producing organic pigment fine particles according to claim 6,wherein the shear rate (U/R) is adjusted to 100 (1/second) or more. 8.The method of producing organic pigment fine particles according toclaim 1, wherein the organic pigment solution is alkaline.
 9. The methodof producing organic pigment fine particles according to claim 1,wherein the organic pigment solution is a homogeneous solution in whichan organic pigment is dissolved in an aqueous organic solvent.
 10. Themethod of producing organic pigment fine particles according to claim 1,wherein the organic pigment solution contains a dispersant.
 11. Themethod of producing organic pigment fine particles according to claim10, wherein at least one dispersant is a low molecular weightdispersant.
 12. The method of producing organic pigment fine particlesaccording to claim 1, wherein the organic pigment fine particles areobtained as a dispersion thereof.
 13. An organic pigment fine particleproduced by the method according to claim 1, having a mode diameter of 1μm or less.